The invention relates to a process and apparatus for the separation of solids from slimy liquids, such as slimy manure, by means of separators in which the pressing power is built up by means of a screw. In particular, the process and apparatus are used for the solid-liquid separation of settled slimy liquid cattle manure and similar suspensions difficult to handle.
The use of liquid manure removal installations has proved itself in the intensive raising of animals, and the method is being applied increasingly. In view of this development, methods were devised for the separation of liquid manure into solids and a liquid phase.
In a report of the Institut fur Technologie der Bundesforschungsanstalt fur Landwirtschaft (Institute for Technology, Federal Research Establishment for Agriculture), Braunschweig-Volkenrode, published in Grundl. Landtechnik, Vol 37 (1987), No 3, pg. 98-107, R. Krause and R. Ahlers described the problem of liquid manure removal and the importance of the solid-liquid separation of liquid manure under the title of "Process Technology of the Separation of Liquid Manure". The advantages and disadvantages of various machines were also set forth and the machines compared with each other.
That publication is the basis of the description of the characteristics of the known technical solutions and the critical analysis presented in the European Patent Application No. 89/119460.7 entitled "Process for the Dewatering of Solids Suspended in Water and a Press Screw Separator Therefor".
The "Journal Series for Concrete Construction Information" of the Beton Publishing Co. also described the principles of separation in a pamphlet entitled "Barn Manure", 1988 pg. 102-106.
However, in actual operation it was found that the value of more than 30% dry substance content required for composting was attained only by decanters and press screw separators of more recent design, and even those machines were not effective with certain types of liquid manure. In particular, with settled liquid cattle manure originating in animal raising facilities with summer grass feeding and similar difficult-to-handle slimy suspensions, known decanters and press screw separators produced no satisfactory results.
In decanters, the slimy substances prevented adequate dewatering even with the use of high centrifugal forces.
In press screw separators, no adequate gravity dewatering through the openings of the screen basket at a corresponding viscosity is obtained, so the slimy mixture cannot be properly seized by the screw for further dewatering in the compression zone.
An object of the present invention is to open up the field of the separation of solids from slimy liquids to screw presses and press screw separators so that these simple and robust machines may be used in a field in which they had heretofore not been capable of use.
The need for the invention arises, because under the conditions of a farming operation, only simple and robust machines may be used, such as machines in which the pressing power is generated by a screw.